The metastatic involvement of lymph nodes is a determining factor for staging various cancers. Although evaluation of all resected material including all lymph nodes and all surrounding biological components having useful information (referred to as “total embedded material”) would be preferred, it is not feasible using conventional techniques because it would require processing hundreds of histology cassettes, many of which would not include any lymph nodes or useful information. Therefore, current approaches focus on identifying and removing lymph nodes from resected fatty tissue. However, there is disagreement as to how many lymph nodes should be evaluated for effective staging. Clinical quality guidelines suggest the evaluation of at least 12 lymph nodes; however, there is increasing acceptance that evaluation of 12 lymph nodes is insufficient for adequate staging. Studies have found that, particularly in patients at stages I-II colon cancer, there is a direct proportional relationship between the number of lymph nodes evaluated and rate of survival.
There are different variables that affect the retrieval of lymph nodes. Among these include effectiveness of the surgeon, the surgery and the pathology exam. Ideally, the surgeon should remove all original lymph nodes pertaining to a tumor, and the pathologist should sample and examine them thoroughly. However, retrieving lymph nodes from resected fatty tissue is time consuming and requires additional training of personnel.
Lymph nodes are conventionally retrieved from fatty tissue using manual palpation with the fingers. To this end, lymph nodes that are more visible and palpable tend to be collected at a higher frequency than those that are smaller. However, some studies suggest that 45%-78% of metastatic lymph nodes have a diameter less than 5 mm, and some metastatic lymph nodes have a diameter even less than 1 mm. As should become apparent, manual palpation is not only laborious but is also prone to error. Studies show that manual palpation methods at best achieve about 50% of lymph nodes from a resected fatty tissue sample, which correlates to a false negative error of 10-35%.
Due to both the importance and challenges associated with retrieving lymph nodes sized at only a few millimeters or less, it has been suggested that fat clearance techniques or the intra-arterial injection of methylene blue may improve identification and retrieval methods; however, even in such instances the staff must work through the entire fatty tissue sample manually to obtain the maximum number of indentifiable lymph nodes, which is usually limited to those sized about 5 mm or greater.
Accordingly, there remains a need to improve the yield of lymph nodes from fatty tissue for histopathological evaluation. Further, there remains a need to decrease the time requirement and skill level required to achieve these higher yields.